The present disclosure relates to a recording apparatus which performs recording with respect to an optical disc recording medium using a so-called adjacent track servo and a control method of the recording apparatus.
As an optical disc recording medium (optical disc) which performs signal recording/reproduction by light illumination, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), a BD (Blu-ray Disc: registered trade mark), or the like has become widespread.
With respect to the optical disc which will be used as a next generation optical disc which is current widespread, such as the CD, the DVD, the BD, or the like, the present inventor first proposed a so-called bulk recording type optical disc as disclosed in Japanese Unexamined Patent Application Publication Nos. 2008-135144 and 2008-176902.
Herein, the bulk recording is a technique for implementing a large recording capacity by performing laser light illumination on a light recording medium (a bulk type recording medium 100), which includes at least a cover layer 101 and a bulk layer (a recording layer) 102, for example, as illustrated in FIG. 13, while sequentially changing the focus position so as to perform multi-layer recording in the bulk layer 102.
With respect to the bulk recording, Japanese Unexamined Patent Application Publication No. 2008-135144 discloses a recording technique which is a so-called micro-hologram scheme.
In the micro-hologram scheme, a so-called hologram recording material is used as a recording material of the bulk layer 102. For example, a photopolymerization type photopolymer or the like is used as the hologram recording material.
The micro-hologram scheme is mainly classified into a positive type micro-hologram scheme and a negative type micro-hologram scheme.
The positive type micro-hologram scheme is a method where a fine interference fringe (hologram) is formed by focusing two opposite light fluxes (light flux A and light flux B) at the same position, and the interference fringe is used as a recording mark.
In addition, as an opposite idea of the positive type micro-hologram scheme, the negative type micro-hologram scheme is a method where an interference fringe which is formed in advance is removed by laser light illumination, and the removed portion is used as a recording mark. More specifically, in the negative type micro-hologram scheme, before the recording operation is performed, an initialization process for forming the interference fringe on the bulk layer 102 in advance is performed. In other words, the illumination of light fluxes C and D as parallel light is performed in the opposite direction, so that the interference fringe is formed on the entire bulk layer 102. Next, after the interference fringe is formed in advance by the initialization process, the information recording is performed through the formation of the erasing mark. More specifically, the laser light illumination according to the to-be-recorded information is performed in the state where focus is aligned at an arbitrary layer position, so that the information recording by the erasing mark is performed.
In addition, as a bulk recording method different from the micro-hologram scheme, the present inventor also proposed a recording method for forming a void (empty hole, empty pore) as a recording mark, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902.
The void recording scheme is a method where the empty hole is recorded in the bulk layer 102 by performing relatively high power laser light illumination on a bulk layer 102 which is configured from a recording material, for example, a photopolymerization type photopolymer, or the like. As disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902, the refractive index of the empty hole portion formed in this manner becomes different from those of other portions in the bulk layer 102, so that the light reflective index of the boundary portion may be increased. Therefore, the empty hole portion functions as a recording mark, so that the information recording is implemented through the formation of the empty hole mark.
In the void recording scheme, since a hologram is not formed, if the light illumination from one side is performed with respect to the recording, the void recording scheme may be considered ineffective. In other words, unlike the case of the positive type micro-hologram scheme, it is not necessary to form the recording mark by focusing the two light fluxes at the same position.
In addition, in comparison with the negative type micro-hologram scheme, there is an advantage in that the initialization process is unnecessary.
In addition, Japanese Unexamined Patent Application Publication No. 2008-176902 discloses an example where the precure light illumination before the recording is performed in the performing of the void recording. However, although the precure light illumination is omitted, the void recording may be performed.
Although the aforementioned various types of recording methods are proposed with respect to the bulk recording type (simply, also referred to as a bulk type) light recording medium, the recording layer (the bulk layer) of the bulk type optical recording medium does not explicitly have a multi-layered structure in the sense that, for example, a plurality of reflective films are formed. In other words, the bulk layer 102 does not include a reflective film and a guiding groove of each recording layer, which are included in a general multi-layered disc.
Therefore, in the state of the structure of the bulk type recording medium 100 illustrated in FIG. 13, the focus servo or the tracking servo may not be performed during the recording period where the mark is not yet formed.
Therefore, in actual cases, a reflection surface (a reference surface Ref) as a reference, which includes guiding grooves illustrated in FIG. 14 is configured to be disposed in the bulk type recording medium 100.
More specifically, the guiding grooves (position guides) such as pits or grooves are formed on the lower surface side of the cover layer 101, and a selective reflection film 103 is formed thereon. In addition, the bulk layer 102 is laminated through an adhesive material, for example, a UV cured resin or the like as an intermediate layer 104 in the figure with respect to the lower surface side of the cover layer 102, where the selective reflection film 103 is formed in this manner.
In addition, after the medium structure is formed, the bulk type recording medium 100 is illuminated with servo laser light as position control laser light separately from mark recording laser light (the recording laser light) as illustrated in FIG. 15.
As illustrated in the figure, the bulk type recording medium 100 is illuminated with the recording laser light and the servo laser light through a common object lens.
At this time, if the servo laser light reaches the bulk layer 102, the servo laser light may have a negative influence on the mark recording in the bulk layer 102. Therefore, in the bulk recording scheme of the related art, laser light having a wavelength band different from that of the recording laser light is used as the servo laser light, and a selective reflection film 103 having a wavelength selectivity where the servo laser light is reflected and the recording laser light is transmitted is disposed as the reflective film which is formed on the guiding groove formation surface (the reference surface Ref).
Under the conditions described hereinbefore, operations during the mark recording period with respect to the bulk type recording medium 100 are described with reference to FIG. 15.
First, when the multi-layer recording is performed on the bulk layer 102 where guiding grooves or a reflective film is not formed, which position is the layer position where the marks are recorded in the depth direction of the bulk layer 102 is set in advance. This figure exemplifies the case where a total of five information recording layer positions L including a first information recording layer position L1 to a fifth information recording layer position L5 are set as the layer positions (mark formation layer positions: also referred to as information recording layer positions) where marks are formed in the bulk layer 102. As illustrated in the figure, the first information recording layer position L1 is set as a position which is separated by a first offset of-L1 in the focus direction (the depth direction) from the selective reflection film 103 (the reference surface Ref) where the guiding grooves are formed. In addition, the second information recording layer position L2, the third information recording layer position L3, the fourth information recording layer position L4, and the fifth information recording layer position L5 are set as positions which are separated by a second offset of-L2, a third offset of-L3, a fourth offset of-L4, and a fifth offset of-L5 from the reference surface Ref, respectively.
During the recording period when the marks are not yet formed, the focus servo and the tracking servo may not be performed on each layer position L as a target in the bulk layer 102 based on the reflected light of the recording laser light. Therefore, the focus servo control and the tracking servo control of the object lens during the recording period is performed so that the spot position of the servo laser light tracks the guiding groove on the reference surface Ref based on the reflected light of the servo laser light as the position control light.
However, the recording laser light necessarily reaches the bulk layer 102 which is formed on the lower surface side from the selective reflection film 103 in order to perform the mark recording. Therefore, in an optical system of this case, a focus mechanism for independently adjusting the focus position of the recording laser light is installed separately from the focus mechanism for the object lens.
Herein, an example of an internal configuration of a recording apparatus for the bulk type recording medium 100 including the mechanism for independently adjusting the focus position of the recording laser light is illustrated in FIG. 16.
In FIG. 16, a first laser diode 111 indicated by LD1 in this figure is a light source of the recording laser light; and a second laser diode 119 indicated by LD2 is a light source of the servo laser light. As understood from the above description, the first laser diode 111 and the second laser diode 119 are configured so as to emit laser light having different wavelength bands.
As illustrated in the figure, the recording laser light emitted from the first laser diode 111 is incident through the collimation lens 112 on a focus mechanism which is constructed with a fixed lens 113, a movable lens 114, and a lens driving unit 115. The movable lens 114 is driven in the direction parallel to the optical axis of the recording laser light by the lens driving unit 115, so that the collimation state (converging/parallel/diverging state) of the recording laser light which is incident on the object lens 117 in this figure is changed. Accordingly, the focus position of the recording laser light may be adjusted independently of a change of the focus position according to the driving of the object lens 117.
In addition, in this sense, the focus mechanism is also referred to as a recording light independent focus mechanism.
The recording laser light passing through the recording light independent focus mechanism is incident on a dichroic mirror 116 which transmits the light having the same wavelength band as that of the recording laser light and reflects the light having the other wavelength bands.
As illustrated in the figure, the bulk type recording medium 100 is illuminated through the object lens 117 with the recording laser light transmitting through the dichroic mirror 116. The object lens 117 is held so that the displacement thereof is performed in the focus direction and the tracking direction by a two-axis actuator 118.
In addition, the servo laser light emitted from the second laser diode 119 passes through the collimation lens 120, and after that, the servo laser light transmits through the beam splitter 121 to be incident on the aforementioned dichroic mirror 116. The servo laser light is reflected on the dichroic mirror 117 so that the optical axis thereof is coincident with the optical axis of the recording laser light transmitting through the dichroic mirror 116, so that the servo laser light is incident on the object lens 117.
The two-axis actuator 118 is driven by the focus servo control according to the later-described servo circuit 125, so that the servo laser light which is incident on the object lens 117 is focused on the selective reflection film 103 (the reference surface Ref) of the bulk type recording medium 100. In addition, at the same time, the two-axis actuator 118 is driven by the tracking servo control according to the servo circuit 125, so that the tracking direction position of the servo laser light tracks the guiding grooves formed on the selective reflection film 103.
The reflected light of the servo laser light from the selective reflection film 103 passes through the object lens 117 and is reflected on the dichroic mirror 116, and after that, the reflected light of the servo laser light is reflected on the beam splitter 121. The reflected light of the servo laser light which is reflected on the beam splitter 121 is collected through a collecting lens 122 on a detection surface of a photodetector 123.
A matrix circuit 124 generates a focus error signal and a tracking error signal based on a light-receiving signal from the photodetector 123 and supplies the error signals to the servo circuit 125.
The servo circuit 125 generates a focus servo signal and a tracking servo signal from the error signals. The aforementioned two-axis actuator 118 is driven based on the focus servo signal and the tracking error signal, so that the focus servo control and the tracking servo control of the object lens 117 are implemented.
Herein, when the mark recording is performed on the necessary information recording layer position L as a target among the information recording layer positions L which are set in advance with respect to the bulk type recording medium 100, the driving of the lens driving unit 115 is controlled, so that the focus position of the recording laser light is changed by the amount corresponding to the offset of which corresponds to the selected information recording layer position L.
More specifically, the control of setting the information recording position is performed, for example, by a controller 126 which performs the overall control of the recording apparatus. In other words, the driving of the lens driving unit 115 is controlled based on the offset amount of-Lx, which is set in advance according to the information recording layer position Lx as a target, by the controller 126, so that the information recording position (the focus position) of the recording laser light is caused to be aligned with the information recording layer position Lx as the aforementioned target.
In addition, as described above, the tracking servo of the recording laser light during the recording period is automatically performed by causing the servo circuit 125 to perform the tracking servo control of the object lens 117 based on the reflected light of the servo laser light. More specifically, the spot position of the recording laser light in the tracking direction is controlled so that the spot position is aligned just below the guiding groove formed on the reference surface Ref.
In addition, when the reproducing is performed with respect to the bulk type recording medium 100 where the mark recording is already performed, similarly to the recording period, the position of the object lens 117 is not necessarily controlled based on the reflected light of the servo laser light from the reference surface Ref. In other words, during the reproduction period, the reproducing laser light illumination is performed on the mark sequence which is formed at the information recording layer position L as a the reproduction target, so that the focus servo control and the tracking servo control of the object lens 117 may be performed based on the reflected light of the reproducing laser light.
As described above, in the bulk recording scheme, it is configured so that the bulk type recording medium 100 is illuminated with the recording laser light as the mark recording light and the servo laser light as the position control light through the common object lens 117 (by combining the recording laser light and the servo laser light on the same optical axis). In addition, the focus servo control and the tracking servo control of the object lens 117 are performed based on the reflected light of the servo laser light, so that it is possible to perform the focus servo and the tracking servo of the recording laser light although the guiding groove or the reflection surface where the guiding groove is formed is not formed in the bulk layer 102.
However, in the case of employing the servo control method described above, there may be a problem in that a shift of the information recording position in the tracking direction occurs due to the lens shift of the object lens 117 which is caused by eccentricity of the bulk type recording medium 100, backlash of the slide mechanism of the optical pickup, or the like.
As described for confirmation, the lens shift according to the backlash of the slide mechanism denotes that, as the position of the optical pickup during the slide servo control is rapidly (instantaneously) changed due to the occurrence of the mechanical backlash of the slide mechanism, the position of the object lens 117 during the tracking servo control is shifted in order to absorb the change thereof.
FIGS. 17A to 17C are diagrams illustrating the principle of the occurrence of the shift of the information recording position according to the lens shift described above.
Among FIGS. 17A to 17C, FIG. 17A illustrates an ideal state where the eccentricity of the bulk type recording medium 100 or the backlash of the slide mechanism does not exist and the lens shift of the object lens 117 does not occur; FIG. 17B illustrates the case where the lens shift in the left direction on the page (referred to as an outer circumference direction) occurs (referred to as an eccentricity in the + direction); and FIG. 17C illustrates the case where the lens shift in the right direction on the page (referred to as an inner circumference direction) occurs (referred to as an eccentricity in the − direction).
First, in these figures, the central axis c is a central axis set for design of an optical system, and in the ideal state illustrated in FIG. 17A, the center of the object lens 117 is coincident with the central axis c.
On the contrary, in the case where the lens shift in the + direction occurs as illustrated in FIG. 17B, the center of the object lens 117 is shifted from the central axis c of the optical system in the + direction.
At this time, since the servo laser light (the patterned light rays in these figures) as parallel light is incident on the object lens 117, although the shift from the central axis c of the object lens 117 occurs as described above, the position change of the focus position in the tracking direction does not occur. On the contrary, since the recording laser light (the outlined light rays in these figures) as non-parallel light is incident on the object lens 117 so as to be focused at the necessary information recording layer position L in the bulk layer 102 of the lower surface side from the reference surface Ref as described above, with respect to the shift of the object lens 117 in the + direction described above, the focus position (the information recording position) of the recording laser light is changed by the distance corresponding to the lens shift amount in the + direction (shift amount+d in the figure) as illustrated in the figure.
In addition, in the case where the lens shift in the − direction occurs as illustrated in FIG. 17C, the information recording position of the recording laser light is changed by a distance corresponding to the lens shift amount in the − direction (shift amount-d in the figure) as illustrated in the figure.
The recording apparatus for the bulk type recording medium 100 described with reference to FIG. 16 has the following configuration.                The illumination of the recording laser light and the servo laser light is performed through the common object lens 117.        The focus servo control of the object lens 117 is performed so that the servo laser light is focused on the reference surface Ref of the bulk type recording medium 100.        The focus position (the information recording position) of the recording laser light is adjusted by changing the collimation state of the recording laser light which is incident on the object lens 117.        The tracking servo control of the object lens 117 is performed so that the focus position of the servo laser light tracks the guiding groove formed on the reference surface Ref.        
In this configuration, there may be a problem in that the shift of the information recording position of the recording laser light occurs in the tracking direction due to the eccentricity of the disc, the backlash of the slide mechanism, or the like.
At this time, there is also a problem in that the information recording positions may be overlapped between the adjacent guiding grooves according to the size of the eccentricity or the like or the setting of the track pitch (the guiding groove formation interval). Therefore, a recording signal may not be correctly reproduced.
In addition, in the above description, although the lens shift of the object lens 117 is described as a main cause of the shift of the information recording position, the shift of the information recording position may also occur in the same manner due to the disc tilt.
As one measure for avoiding the aforementioned problems of the shift of the information recording position, the track pitch is widened so as be equal to or larger than the change in the information recording position.
However, in this measure, since the maximum amount of the lens shift or the like is not definitely determined, there may be a problem where it is not determined to what extent the track pitch is to be widened. In addition, above all, there may be a problem in that the recording capacity is decreased due to the widening of the track pitch.
In addition, as another measure for avoiding the shift of the information recording position, the system is configured so that the disc is non-detachable.
Herein, as a cause of the eccentricity, there is an error between an inner diameter of a disc and a clamp diameter of a spindle motor. In the manufacturing process, it is difficult to completely remove the error therebetween so as to be zero, so that the eccentricity is inevitable. In addition, even though the error therebetween may be removed so as to be zero, since the recording signal center of the reference surface of the disc may not be coincident with the spindle shaft center of the recording apparatus, the eccentricity also occurs on the surface. Therefore, if the system is configured so that the disc is non-detachable, the influence of the eccentricity is the same, so that it is possible to avoid the problem of recording positions overlapping. Accordingly, the track pitch may be reduced, so that it is possible to increase the recording capacity by the amount corresponding to the reduction of the track pitch.
However, naturally, since the replacement of the disc may not be performed in this method, for example, when the disc is defective, the replacement of only the disc may not be performed. In addition, reading of data recorded in the recording apparatus may not be performed by another recording apparatus. In other words, in this sense, the convenience is lost.
Therefore, as an effective method for avoiding this problem, it is considered to employ the so-called ATS (Adjacent Track Servo) method. Originally, the ATS has been investigated as a self servo track writer in a hard disk drive.
FIG. 18 is a diagram illustrating the ATS.
As illustrated in this figure, in the ATS, a recording spot Srec and an adjacent track servo spot Sats are configured to be formed on the recording medium. The spot Srec and the spot Sats are formed by illuminating the recording medium through the common object lens with light beams as respective light sources. At this time, the distance between the spots is set to be fixed.
In the ATS, the recording spot Srec is set as a preceding spot (that is, in the case where the recording proceeding direction is inner circumference outer circumference, the outer circumference side spot), and the adjacent track servo spot Sats is set as the following spot which is in the mark sequence formed by the recording spot Srec. The tracking servo is applied by the adjacent track servo spot Sats. As a result, the tracking servo control of the object lens is performed so that the adjacent track servo spot Sats tracks the one preceding track where the recording spot Srec is formed.
According to the ATS, since the track pitch as the distance between the spots S is constant, it is possible to prevent the occurrence of the problem where the tracks are overlapped (the information recording positions are overlapped) due to the influence of the eccentricity or the like. In other words, as described above, it is not necessary to increase the track pitch marginally or to configure a system where the disc may not be mounted by considering the shift of the information recording position caused by the eccentricity or the like.